Hydraulic systems utilizing a pressurized fluid through a series of pistons is generally known in the art. Typically, it is important to have these pistons synchronized with respect to one another. In other words, it is desirable to have these pistons reach the top and the bottom of their respective strokes at the same time. This can be especially desirable when raising and lowering components of a piece of equipment.
During use of these types of hydraulic systems the pistons may get out of sync due to the wear of various parts on the pistons. Most commonly, seals can wear and begin to degrade over time allowing the fluid within the system to bypass the pistons and leak out of the system. When the fluid is removed from the system, by leaking or otherwise, a decrease in pressure within the system occurs causing the pistons to travel at varying speeds thereby causing the pistons to begin and end their strokes at different times. In applications such as those described above, i.e. raising and lowering components of equipment, the variation in piston movement will not allow the components of the move smoothly and safely. To remedy this problem, the pistons need to be resynced. The process of resyncing the pistons is commonly known in the art as rephasing.
There have been various attempts in the prior art to rephase hydraulic systems. One such system disclosed in U.S. Pat. No. 3,832,852 to Schmucker requires that a groove be placed on the interior surface of the cylinder wall to allow fluid to bypass the cylinder when the piston is in a rephasing position. With such a design, the seal around the piston has a tendency to deform into the groove as the piston moves past the groove. Over time the portion of the deformed seal will shear off and not allow that cylinder to maintain pressure therein.
Another design taught in U.S. Pat. No. 7,537,079 to Krieger et al. requires a longitudinal hole defined by a face of the piston that meets a radial hole defined by a side face of the piston, creating a passageway through the piston. A check valve is place within the passage way to automatically allow fluid to flow from a first cylinder to a second cylinder, but not from the second cylinder back to the first cylinder. Although effective to rephase the hydraulic system, this design is cumbersome and expensive to manufacture.
Therefore there remains a need in the art for a hydraulic system that will allow the pistons to be automatically rephased and is both easy to use and inexpensive to manufacture.